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Award Ceremony Speech

This year's Nobel Prize for Physics has been awarded to Professor
Klaus von Klitzing for the discovery of the quantized Hall
effect.

This discovery is an example of these
unexpected and surprising discoveries that now and then take
place and which make research in the sciences so exciting. The
Nobel Prize is sometimes an award given to large projects, where
one has shown great leadership and where one with ingenuity
combined with large facilities and material resources has
experimentally verified the correctness of theoretical models and
their predictions. Or, one has succeeded through creation of new
theoretical concepts and methods to develop theories for
fundamental problems in physics that resisted all theoretical
attempts over a long period of time. However, now and then things
happen in physics that no one can anticipate. Someone discovers a
new phenomenon or a new fundamental relation in areas of physics
where no one expects anything exciting to happen.

This was exactly what happened when Klaus
von Klitzing in February 1980 was working on the Hall effect at
the Hochfelt-Magnet-Labor in Grenoble. He discovered from his
experimental data that a relation which had been assumed to hold
only approximately seemed to hold with an exceptionally high
accuracy and in this way the discovery of the quantized Hall
effect was made.

The discovery by von Klitzing has to do
with the relation between electric and magnetic forces in nature
and has a long history. Let us go back to 1820, when the Danish
physicist H.C. Ørsted found that an electric current in a
wire influenced a compass needle and made it change its
direction. He discovered this phenomenon in a class with his
students. No one had seen a relation between electric and
magnetic forces before. More than 50 years later a young American
physicist, E.H. Hall, speculated that the magnetic force might
influence the charge carriers in a metallic wire placed in a
magnetic field and give rise to an electric voltage across the
wire. He was able to show that when sending an electric current
through a strip of gold there was a small voltage across the wire
in a direction perpendicular both to the current and the magnetic
field. That was the discovery of the Hall effect.

The Hall effect is now a standard method
frequently used to study semiconductor materials of technical
importance, and the effect is described in all textbooks in solid
state physics. The experiment is in principle very simple and
requires only a magnetic field plus instruments to measure
current and voltage. If one varies the magnetic field, the
current and voltage will change in a completely regular way and
no surprising effects are expected to happen.

von Klitzing studied the Hall effect under
quite extreme conditions. He used an extremely high magnetic
field and cooled his samples to just a couple of degrees above
the absolute zero point of temperature. Instead of the regular
change one would expect, he found some very characteristic steps
with plateaus in the conductivity. The values at these plateaus
can with extremely high accuracy be expressed as an integer times
a simple expression that just depends of two fundamental
constants: the electric elementary charge and Planck's constant
which appear everywhere in quantum physics.

The result represents a quantization of the
Hall effect - a completely unexpected effect. The accuracy in his
results was about one part in ten million, which would correspond
to measuring the distance between Stockholm and von Klitzing's
home station Stuttgart with an accuracy of a few centimeters. The
discovery of the quantized Hall effect is a beautiful example of
the close interrelation between the highly advanced technology in
the semiconductor industry and fundamental research in physics.
The samples used by von Klitzing were relined versions of a kind
of transistor we have in our radios. His samples, however, had to
satisfy extremely high standards of perfection and could only be
made by using a highly advanced technique and refined
technology.

The quantized Hall effect can only be
observed in a two-dimensional electron system. Two-dimensional
electron systems do not occur in nature. However, the development
in semiconductor technology has made possible the realization of
a two-dimensional electron system. In the kind of transistor that
von Klitzing used, some of the electrons are bound to the
interface between two parts of the transistor. At sufficiently
low temperature the electrons can move only along the interface
and one has effectively a two-dimensional electron system.

von Klitzing's discovery of the quantized
Hall effect attracted immediately an enormous interest. Because
of the extremely high accuracy the effect can be used to define
an international standard for electric resistance. The
metrological possibilities are of great importance and have been
subject to detailed studies at many laboratories all over the
world.

The quantized Hall effect is one of the few
examples, where quantum effects can be studied in ordinary
macroscopic measurements. The underlying detailed physical
mechanisms are not yet fully understood. Later experiments have
revealed completely new and unexpected properties and the study
of two-dimensional systems is now one of the most challenging
areas of research in physics.

Professor von Klitzing,

On behalf of the Royal Swedish Academy of Sciences I wish to
convey our warmest congratulations and ask you to receive your
prize from the hands of His Majesty the King.